Method and arrangement for determining transmission delay differences

ABSTRACT

The invention relates to determining mutual differences of transmission delays experienced by protocol data units transmitted in a communications network. This invention is based on a surprising discovery that the time difference between the receiving moments of protocol data units the temporal receiving order of which deviates from their temporal transmitting order represents the smallest possible difference between the transmission delays experienced by these protocol data units. In a method according to the invention it is determined, based on an order indicator associated with a protocol data unit received at an earlier point of time and an order indicator associated with a protocol data unit received at a later point of time, whether the mutual order of the protocol data units changed during transmission. If the mutual order has changed, the time difference between the receiving moments of the protocol data units is calculated, which time difference represents the smallest possible difference between the transmission delays experienced by these protocol data units.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a new division of co-pending application Ser. No.12/361,065 filed on Jan. 28, 2009, which claims priority to FinnishApplication No. 20080066 filed on Jan. 29, 2008. The entire contents ofeach of the above-identified applications are hereby incorporated byreference.

FIELD OF THE INVENTION

The invention relates to determining the mutual differences oftransmission delays experienced by protocol data units. The inventionconcerns a method and an arrangement for determining the mutualdifferences of transmission delays experienced by protocol data unitsreceived. The invention further concerns a network element and acomputer program.

BACKGROUND OF THE INVENTION

In many telecommunications applications it is advantageous or evennecessary that the mutual differences of the transmission delays ofprotocol data units belonging to a communications stream remain withinacceptable limits. Such protocol data units may be e.g. IP (InternetProtocol) packets, ATM (Asynchronous Transfer Mode) cells, Ethernetunits, or Frame Relay units. Said communications stream is typicallycomprised of protocol data units transmitted consecutively in time. Forexample, in a situation where the communications stream is carrying avoice and/or video signal, variation in the transmission delay willincrease the need for buffering the data packets received at thereceiving network element such as a router, for instance. Buffering willincrease the total delay experienced by said communications stream whileit should be as small as possible. In connectionless communicationssystems, different data protocol units of the communications stream maytravel through different routes on their way from the source networkelement to the destination network element. This means that differingtransmission delays experienced by the various data protocol units mayresult in changing the mutual temporal order between the data protocolunits, ie. the receiving order of the data protocol units deviates fromthe temporal order of transmission of the protocol data units inquestion. Also, in connection-based communications systems, thecommunications stream is often directed to travel along two or moreparallel routes, e.g. for the reason of exercising load balancingbetween the different parts of the communications network. Changes inthe mutual temporal order of the data protocol units will increase theneed for buffering the data protocol units received.

The mutual differences of the transmission delays experienced by thedata protocol units should be somehow determined so that it is possibleto take corrective action as needed. Said corrective action may consistof, for example, configuring the routing protocol in such a way thatparts or areas of the communications network which cause a lot oftransmission delay are replaced by other parts or areas of thecommunications network, and/or the quality classification of parts orareas of the communications network which cause a lot of transmissiondelay is downgraded in order for a quality classification aware routingprotocol to be able to avoid using those parts or areas.

In a prior-art method, a quantity indicating the variation in thetransmission delay is calculated based on the transmission and receptiontimes of the protocol data units. To illustrate the method, let usexamine two data protocol units PDU1 and PDU2. Protocol data unit PDU1has been sent from the source network element at moment t_tx1, andprotocol data unit PDU2 has been sent at t_tx2. Protocol data unit PDU1was received in the destination network element at moment t_rx1, andprotocol data unit PDU2 was received at t_rx2. The transmission delayexperienced by protocol data unit PDU1 is d1=t_rx1−t_tx1, and thetransmission delay experienced by protocol data unit PDU2 isd2=t_rx2−t_tx2. The quantity indicating the difference between the twotransmission delays is the differenced1−d2=(t_rx1−t_tx1)−(t_rx2−t_tx2)=(t_rx1−t_rx2)−(t_tx1−t_tx2). Thelatter of the expressions representing the difference of thetransmission delays shows that the clocks in the source network elementand destination network element need not have a common time, but itsuffices that said clocks are mutually frequency-locked, ie. are runningat the same rate. In addition to the prerequisite concerning thefrequency lock between the clocks the method also requires that thequantity indicating the transmission moment of each protocol data unitis transmitted to the destination network element. In manycommunications applications, however, these demands are not met.

SUMMARY

The invention is directed at an arrangement for determining the mutualdifferences of transmission delays experienced by protocol data unitsreceived and for performing control actions related to ingress ports ofa network element. Each protocol data unit is associated with an orderindicator arranged to indicate the position of the protocol data unit inthe mutual sequential order of said protocol data units. A givenprotocol data unit is transmitted earlier than or simultaneously withthe protocol data unit next in said sequential order. The orderindicator need not be a piece of information indicating the transmittingmoment of a protocol data unit, but it suffices that said orderindicator is, for example, an ordinal number attached to the protocoldata unit, or a letter of the alphabet complying with the alphabeticalorder, or some other piece of information which indicates the positionof the protocol data unit in said sequential order. An arrangementaccording to the invention has a processor unit arranged to:

-   -   determine, based on a first order indicator associated with a        first protocol data unit received earlier and a second order        indicator associated with a second protocol data unit received        later, whether the first protocol data unit is later in said        sequential order than said second protocol data unit, said first        protocol data unit being a protocol data unit received at a        first ingress port of the network element, and said second        protocol data unit being a protocol data unit received at a        second ingress port of said network element,    -   in response to a situation in which said first protocol data        unit is later in said sequential order than said second protocol        data unit, calculate the time difference of the receiving        moments of said second protocol data unit and said first        protocol data unit, said time difference representing a lower        limit for a difference between the transmission delays        experienced by said second protocol data unit and said first        protocol data unit, and    -   downgrade a quality classification associated with said second        ingress port and used by a quality classification aware routing        protocol in response to a situation where said first protocol        data unit is later in said sequential order than said second        protocol data unit and an indicator value updated on the basis        of said time difference exceeds a predetermined threshold value.

The invention is also directed to a network element comprising a firstingress port and a second ingress port for receiving protocol dataunits. Each protocol data unit is associated with an order indicatorarranged to indicate the position of the protocol data unit in themutual sequential order of said protocol data units, and each protocoldata unit is sent earlier than or simultaneously with the protocol dataunit next in said sequential order. A network element according to theinvention has a processor unit arranged to:

-   -   determine, based on a first order indicator associated with a        first protocol data unit received earlier and a second order        indicator associated with a second protocol data unit received        later, whether the first protocol data unit is later in said        sequential order than said second protocol data unit, said first        protocol data unit being a protocol data unit received at the        first ingress port of the network element, and said second        protocol data unit being a protocol data unit received at the        second ingress port of the network element,    -   in response to a situation in which said first protocol data        unit is later in said sequential order than said second protocol        data unit, calculate the time difference of the receiving        moments of said second protocol data unit and said first        protocol data unit, said time difference representing a lower        limit for a difference between the transmission delays        experienced by said second protocol data unit and said first        protocol data unit, and    -   downgrade a quality classification associated with said second        ingress port and used by a quality classification aware routing        protocol in response to a situation where said first protocol        data unit is later in said sequential order than said second        protocol data unit and an indicator value updated on the basis        of said time difference exceeds a predetermined threshold value.

The invention is also directed to a method for determining the mutualdifferences of transmission delays experienced by protocol data unitsreceived and for performing control actions related to ingress ports ofa network element. Each protocol data unit is associated with an orderindicator arranged to indicate the position of the protocol data unit inthe mutual sequential order of said protocol data units, and eachprotocol data unit is sent earlier than or simultaneously with theprotocol data unit next in said sequential order. In a method accordingto the invention:

-   -   it is determined, based on a first order indicator associated        with a first protocol data unit received earlier and a second        order indicator associated with a second protocol data unit        receiver later, whether the first protocol data unit is later in        said sequential order than said second protocol data unit, said        first protocol data unit being a protocol data unit received at        a first ingress port of the network element and said second        protocol data unit is a protocol data unit received at a second        ingress port of the network element,    -   in response to a situation in which said first protocol data        unit is later in said sequential order than said second protocol        data unit, it is calculated the time difference of the receiving        moments of said second protocol data unit and said first        protocol data unit, said time difference representing a lower        limit for a possible difference between the transmission delays        experienced by said second protocol data unit and said first        protocol data unit, and    -   a quality classification associated with said second ingress        port and used by a quality classification aware routing protocol        is downgraded in response to a situation where said first        protocol data unit is later in said sequential order than said        second protocol data unit and an indicator value updated on the        basis of said time difference exceeds a predetermined threshold        value.

The invention is also directed to a computer program for controlling aprogrammable processor to determine the mutual differences of thetransmission delays experienced by protocol data units received and toperform control actions related to ingress ports of a network element,wherein each protocol data unit is associated with an order indicatorarranged to indicate the position of the protocol data unit in themutual sequential order of said protocol data units, and each protocoldata unit is sent earlier than or simultaneously with the protocol dataunit next in said sequential order. A computer program according to theinvention has:

-   -   software means for controlling said programmable processor to        determine, based on a first order indicator associated with a        first protocol data unit received earlier and a second order        indicator associated with a second protocol data unit received        later, whether said first protocol data unit is later in said        sequential order than said second protocol data unit, said first        protocol data unit being a protocol data unit received at a        first ingress port of the network element to be controlled, and        said second protocol data unit being a protocol data unit        received at a second ingress port of the network element,    -   software means for controlling said programmable processor to        calculate, in response to a situation in which said first        protocol data unit is later in said sequential order than said        second protocol data unit, the time difference of the receiving        moments of said second protocol data unit and said first        protocol data unit, said time difference representing the        smallest possible difference between the transmission delays        experienced by said second protocol data unit and said first        protocol data unit, and    -   software means for controlling said programmable processor to        downgrade a quality classification associated with said second        ingress port and used by a quality classification aware routing        protocol in response to a situation where said first protocol        data unit is later in said sequential order than said second        protocol data unit and an indicator value updated on the basis        of said time difference exceeds a predetermined threshold value.

The various embodiments of the invention are characterized by that whichis specified in the dependent claims.

Embodiments of the invention provide an advantage over the prior-artsolution described in this document, which advantage means that theclock in the destination network element need not be frequency-lockedwith the clock in the source network element and, furthermore, there isno need to transmit information indicating the transmitting moment ofeach protocol data unit to the destination network element. If theinformation indicating the transmitting moment is available to thedestination network element it can used as an order indicator attachedto the protocol data unit.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention and their advantages will now be describedin closer detail with reference to the embodiments presented by way ofexample and to the accompanying Figures where:

FIG. 1 illustrates in block diagram a telecommunications systememploying an arrangement according to an embodiment of the invention fordetermining the mutual differences of transmission delays experienced byprotocol data units received,

FIG. 2 illustrates in block diagram a telecommunications systememploying an arrangement according to an embodiment of the invention fordetermining the mutual differences of transmission delays experienced byprotocol data units received,

FIG. 3 illustrates in block diagram a network element according to anembodiment of the invention, and

FIG. 4 illustrates in flow diagram a method according to an embodimentof the invention for determining the mutual differences of transmissiondelays experienced by protocol data units received.

DESCRIPTION OF EMBODIMENTS OF INVENTION

FIG. 1 illustrates in block diagram a telecommunications systememploying an arrangement according to an embodiment of the invention fordetermining the mutual differences of transmission delays experienced byprotocol data units received. Protocol data units 130, 131, 132, 133, .. . belonging to a communications stream are transmitted from a sourcenetwork element 101 to a destination network element 102 via acommunications network 103. The protocol data units are transmittedusing two parallel routes 110 and 111 such that protocol data unit 130,for example, is sent through egress port 104 onto route 110 and protocoldata unit 131, for example, is sent through egress port 105 onto route111. Protocol data unit 130 is received at ingress port 106 of thedestination network element 102, and protocol data unit 131 is receivedat ingress port 107 of the destination network element. In thecommunications system illustrated in FIG. 1, egress ports 104 and 105 aswell as ingress ports 106 and 107 are depicted as physical ports. FIG. 2shows an example using logical ports. Protocol data unit 130′ representsprotocol data unit 130 after protocol data unit 130 has been transmittedfrom the source network element 101 to the destination network element102. Similarly, protocol data unit 131′ represents protocol data unit131 after protocol data unit 131 has been transmitted from the sourcenetwork element 101 to the destination network element 102. The protocoldata units may be e.g. IP (Internet Protocol) packets, ATM (AsynchronousTransfer Mode) cells, Ethernet units, or Frame Relay units.

Each protocol data unit 130, 131, 132, 133, . . . is associated with anorder indicator arranged to indicate the position of the protocol dataunit in the mutual sequential order of said protocol data units. Theorder indicator may be e.g. a transmission time stamp, which indicatesthe transmitting moment of the protocol data unit, ordinal number of theprotocol data unit, or some other symbol attached to the protocol dataunit, which symbol follows a predetermined order, such as a letter ofthe alphabet following the alphabetical order. The order indicatorenables the destination network element to reconstruct the originalsequential order of the protocol data units even if the temporalreceiving order of the protocol data units were not the same as theoriginal sequential order. A given protocol data unit in the sourcenetwork element is transmitted earlier than or simultaneously with theprotocol data unit next in said sequential order. In the exampledepicted in FIG. 1, protocol data unit 131 is after protocol data unit130 in said sequential order. Protocol data units 130 and 131 in thesource network element 101 are transferred to the egress ports 104 and105 either substantially simultaneously or in such a manner thatprotocol data unit 130 is taken to egress port 104 earlier than protocoldata unit 131 to egress port 105.

The arrangement for determining the mutual differences of transmissiondelays experienced by received protocol data units employs a processorunit 108 arranged to:

-   -   determine, based on a first order indicator associated with a        first protocol data unit received earlier and a second order        indicator associated with a second protocol data unit received        later, whether the first protocol data unit is later in said        sequential order than said second protocol data unit, and    -   in response to a situation in which said first protocol data        unit is later in said sequential order than said second protocol        data unit, calculate the time difference of the receiving        moments of said second protocol data unit and said first        protocol data unit.

Said time difference represents the smallest possible difference betweenthe transmission delays experienced by said second protocol data unitand said first protocol data unit.

To illustrate the operation of the arrangement let us consider anexemplary situation in which protocol data unit 131′ has been receivedearlier than protocol data unit 130′. On the other hand, in thesequential order of protocol data units, protocol data unit 131′ islater than protocol data unit 130′, as indicated by the orderindicators. So we have a situation in which a first protocol data unit(131′) received earlier is later in the sequential order than a secondprotocol data unit (130′) received later. Without limiting thegenerality we can assume that:

-   -   transmitting moment of protocol data unit 130′ (130) from the        source network element 101 is t_tx1,    -   transmitting moment of protocol data unit 131′ (131) from the        source network element 101 is t_tx2,    -   receiving moment of protocol data unit 130′ (130) at the        destination network element 102 is t_rx1, and    -   receiving moment of protocol data unit 131′ (131) at the        destination network element 102 is t_rx2.

Since it is assumed that protocol data unit 131′ is received earlierthan protocol data unit 130, t_rx1>t_rx2. Furthermore, t_tx2≧t_tx1,because in the sequential order of protocol data units, protocol dataunit 131′ is later than protocol data unit 130′. The transmission delayexperienced by protocol data unit 130′ is d1=t_rx1−t_tx1, and thetransmission delay experienced by protocol data unit 131′ isd2=t_rx2−t_tx2. The quantity indicating the difference between the twotransmission delays d1 and d2 is the difference of said transmissiondelays:d1−d2=(t_rx1−t_tx1)−(t_rx2−t_tx2),  (1)which can be expressed as:d1−d2 =(t_rx1−t_rx2)+(t_tx2−t_tx1),  (2)

For the transmission delay difference d1−d2,d1−d2≧t_rx1−t_rx2,  (3)since t_tx2≧t_tx1, or t_tx2−t_tx1≧0 (in the sequential order of protocoldata units, protocol data unit 131′ is later than protocol data unit130′). Therefore, the time difference between the receiving moments ofprotocol data unit 130′, received later, and protocol data unit 131′,received earlier, represents the smallest possible difference betweenthe transmission delays d1 and d2. Said time difference equals thedifference between the transmission delays if protocol data units 130′and 131′ are transmitted simultaneously. As equation 3 shows, there isno need to know the transmitting moments t_tx1 and t_tx2.

As can be seen from the above example, the time difference t_rx1−t_rx2between the receiving moments indicates the smallest possible differencebetween the transmission delays d1 and d2 if the receiving order of theprotocol data units deviates from the sequential order of the protocoldata units as defined by the order indicators. In other words, thetemporal order of the protocol data units has changed duringtransmission. The above principle can be applied to the detection of theamount of delay variation in the communications stream if there is apossibility that the temporal order of protocol data units can changeduring transmission and said protocol data units have a sequential orderindicated to the destination network element. The principle can beapplied to comparing the delay properties of sub-streams of acommunications stream by selecting a first protocol data unit from afirst sub-stream and a second protocol data unit from a secondsub-stream. Sub-streams can be represented by protocol data unitsarriving at different physical or logical ingress ports, for example. Inthe above example, the smallest possible difference between thetransmission delays was determined in a situation where the firstprotocol data unit belongs to a first sub-stream of a communicationsstream arriving at a first ingress port 107, and the second protocoldata unit belongs to a second sub-stream of the same communicationsstream arriving at a second ingress port 106.

The above principle can also be applied in a situation where protocoldata units representing a communications stream arrive at more than twoingress ports. Let us assume, for example, that a communications streamarrives at ingress ports P1, P2, . . . , PN. In a situation where aprotocol data unit PDU(a) arrives at ingress port Pi and protocol dataunit PDU(b) arrives at ingress port Pj and the temporal order of theseprotocol data units PDU(a) and PDU(b) has changed, we get a quantityindicating the transmission delay difference of the transmission routesassociated with said ingress ports Pi and Pj (the time differencebetween the receiving moments of PDU(a) and PDU(b)), where i=1 to N andj=1 to N. In other words, we get quantities indicating the transmissiondelay difference of the transmission routes for all ingress port pairsPi, Pj. By examining the quantities measured for the different ingressport pairs indicating the transmission delay difference it is possiblee.g. to identify the ingress port(s) whose route(s) cause(s) the mosttransmission delay.

The receiving moments of protocol data units can be measured using aclock signal produced by a clock generator 109. In the communicationssystem depicted in FIG. 1 the clock generator is part of the destinationnetwork element 102. The receiving moments of protocol data units canalso be measured using a clock signal received from outside thedestination network element 102.

In an arrangement according to an embodiment of the invention aprocessor unit 108 is arranged to remove ingress port 106 from among theingress ports available to the routing protocol in response to asituation where a protocol data unit 131′, which is received earlier, islater in the sequential order, based on order indicators, than protocoldata unit 130′, which is received later, and an indicator value updatedon the basis of the time difference between the receiving moments of theprotocol data units 130′ and 131′ exceeds a predetermined thresholdvalue. Route 110 thus causes bigger transmission delays than route 111.Said routing protocol may be, for example, an IP (Internet Protocol)routing protocol by means of which the source network element 101,destination network element 102, and network elements of thecommunications network 103 maintain their routing tables. In anarrangement according to another embodiment of the invention a processorunit 108 is arranged to downgrade the quality classification associatedwith ingress port 106 and used by a quality class aware routing protocolin response to a situation where a protocol data unit 131′, which isreceived earlier, is later in the sequential order, based on orderindicators, than protocol data unit 130′, which is received later, andan indicator value updated on the basis of the time difference betweenthe receiving moments of the protocol data units 130′ and 131′ exceeds apredetermined threshold value. In other words, the routing protocol isconfigured in such a way that parts or areas of the communicationsnetwork 103 which cause a lot of transmission delay are replaced byother parts or areas of the communications network, and/or the qualityclassification of parts or areas of the communications network whichcause a lot of transmission delay is downgraded in order for a qualityclassification aware routing protocol to be able to avoid using thoseparts or areas.

The procedure applied in the update of said indicator value can bechosen in several different ways. For instance, the processor unit 108may be arranged to compare the time difference between the receivingmoments to a previous indicator value and make said time differencebetween the receiving moments the new indicator value in response to asituation where said time difference between the receiving moments and apredetermined number (0 to N) of previously calculated correspondingtime differences between the receiving times exceed said previousindicator value. For example, the processor unit 108 may be arranged touse the plain time difference between the receiving moments as saidindicator value. The processor unit 108 may be arranged, for example, touse the time difference between the receiving moments as an inputquantity for low-pass filtering, and an output quantity of said low-passfiltering as said indicator value.

FIG. 2 illustrates in block diagram a telecommunications systememploying an arrangement according to an embodiment of the invention fordetermining the mutual differences of transmission delays experienced byprotocol data units received. Protocol data units 230, 231, 232, 233, .. . belonging to a communications stream are transmitted from a sourcenetwork element 201 to a destination network element 202 via acommunications network 203. Some of the protocol data units aretransmitted via logical egress port 212 of the source network element201 and some via logical egress port 213. Protocol data unitstransmitted through logical egress port 212 are routed onto route 210between network elements 221 and 222 and received at logical ingressport 214 of the destination network element 202. Protocol data unitstransmitted through logical egress port 213 are routed onto route 211between network elements 221 and 222 and received at logical ingressport 215 of the destination network element 202. The mutual order ofprotocol data units 230, 231, 232, 233, . . . may change in thetransmission between the network elements 221 and 222. Logical egressports 212 and 213 are implemented in physical egress port 204 andlogical ingress ports 212 and 213 are implemented in physical ingressport 207. A logical port may be represented e.g. by an IP tunnel, ATM-VC(Asynchronous Transfer Mode—Virtual Circuit), MPLS-LSP (MultiProtocolLabel Switching—Label Switched Path), or some other predetermined linkin the communications network. Protocol data unit 230′ representsprotocol data unit 230 after protocol data unit 230 has been transmittedfrom the source network element 201 to the destination network element202. Similarly, protocol data unit 231′ represents protocol data unit231 after protocol data unit 231 has been transmitted from the sourcenetwork element 201 to the destination network element 202.

Each protocol data unit 230, 231, 232, 233, . . . is associated with anorder indicator arranged to indicate the position of the protocol dataunit in the mutual sequential order of said protocol data units. A givenprotocol data unit in the source network element is transmitted earlierthan or simultaneously with the protocol data unit next in saidsequential order. In the example depicted in FIG. 2, protocol data unit231 is later than protocol data unit 230 in said sequential order.

The arrangement for determining the mutual differences of transmissiondelays experienced by received protocol data units employs a processorunit 208 arranged to:

-   -   determine, based on a first order indicator associated with a        first protocol data unit (230′ or 231′) received earlier and a        second order indicator associated with a second protocol data        unit (231′ or 230′) received later, whether the first protocol        data unit is later in said sequential order than said second        protocol data unit, and    -   in response to a situation in which said first protocol data        unit is later in said sequential order than said second protocol        data unit, calculate the time difference of the receiving        moments of said second protocol data unit and said first        protocol data unit.

Said time difference represents the smallest possible difference betweenthe transmission delays experienced by said second protocol data unit(231′ or 230′) and said first protocol data unit (230′ or 231′).

FIG. 3 is a block diagram illustrating a network element 300 accordingto an embodiment of the invention, which network element may be e.g. anIP router, Ethernet switch, ATM switch, base station of a mobilecommunications network, or an MPLS switch. The network element isadapted to receive protocol data units 330, 331. Each protocol data unitis associated with an order indicator arranged to indicate the positionof the protocol data unit in the mutual sequential order of saidprotocol data units, and each protocol data unit is sent earlier than orsimultaneously with the protocol data unit next in said sequentialorder. The network element has a processor unit 308 arranged to:

-   -   determine, based on a first order indicator associated with a        first protocol data unit received earlier and a second order        indicator associated with a second protocol data unit received        later, whether the first protocol data unit is later in said        sequential order than said second protocol data unit, and    -   in response to a situation in which said first protocol data        unit is later in said sequential order than said second protocol        data unit, calculate the time difference of the receiving        moments of said second protocol data unit and said first        protocol data unit, said time difference representing the        smallest possible difference between the transmission delays        experienced by said second protocol data unit and said first        protocol data unit.

Without limiting the generality, we can assume that said first protocoldata unit is protocol data unit 331 and said second protocol data unitis protocol data unit 330.

In a network element according to an embodiment of the invention saidfirst protocol data unit is a protocol data unit received at a firstingress port 307 of said network element, and said second protocol dataunit is a protocol data unit received at a second ingress port 306 ofsaid network element. Ingress port 306 may be a physical or a logicalingress port. Similarly, ingress port 307 may be a physical or a logicalingress port.

In a network element according to an embodiment of the invention saidprocessor unit 308 is arranged to remove ingress port 306 from among theingress ports available to the routing protocol in response to asituation where a protocol data unit 331, which is received earlier, islater in the sequential order according to order indicators thanprotocol data unit 330, which is received later, and an indicator valueupdated on the basis of the time difference between the receivingmoments of the protocol data units 330 and 331 exceeds a predeterminedthreshold value. As expressed in the description of FIG. 1, theprocedure applied in the update of said indicator value can be chosen inseveral different ways.

In a network element according to an embodiment of the invention saidprocessor unit 308 is arranged to downgrade the quality classificationwhich is associated with ingress port 306 and used by a qualityclassification aware routing protocol, in response to a situation wherea protocol data unit 331, which is received earlier, is later in thesequential order, which is based on order indicators, than protocol dataunit 130, which is received later, and an indicator value updated on thebasis of the time difference between the receiving moments of theprotocol data units 330 and 331 exceeds a predetermined threshold value.

A network element according to an embodiment of the invention has aprocessor for executing said routing protocol. Said processor may beprocessor unit 308 or some other processor in the network element. Anetwork element according to an embodiment of the invention has anegress port 324 for supplying data indicating mutual differences oftransmission delays to external hardware.

A network element according to an embodiment of the invention has aclock generator 309 arranged to produce a clock signal for measuring thereceiving moments of protocol data units. A network element according toan embodiment of the invention has an ingress port 323 for receiving aclock signal from outside the network element.

FIG. 4 illustrates in flow diagram a method according to an embodimentof the invention for determining the mutual differences of transmissiondelays experienced by protocol data units received. Each protocol dataunit is associated with an order indicator arranged to indicate theposition of the protocol data unit in the mutual sequential order ofsaid protocol data units, and each protocol data unit is sent earlierthan or simultaneously with the protocol data unit next in saidsequential order. In step 401 it is determined the mutual order of afirst protocol data unit, which is received earlier, and a secondprotocol data unit, received later, in said sequential order, based on afirst order indicator associated with said first protocol data unit anda second order indicator associated with said second protocol data unit.If said first protocol data unit is later in said sequential order thansaid second protocol data unit, the method proceeds to step 402 where itis calculated the time difference of the receiving moments of saidsecond protocol data unit and said first protocol data unit. Said timedifference represents the smallest possible difference between thetransmission delays experienced by said second protocol data unit andsaid first protocol data unit.

In a method according to an embodiment of the invention said firstprotocol data unit is a protocol data unit received at a first ingressport of a network element, and said second protocol data unit is aprotocol data unit received at a second ingress port of said networkelement. Said first ingress port may be a physical or a logical ingressport, and said second ingress port may be a physical or a logicalingress port.

In a method according to an embodiment of the invention, said secondingress port is removed from among the ingress ports available to therouting protocol if said first protocol data unit, received at anearlier point of time, is later in said sequential order than saidsecond protocol data unit, received at a later point of time, and anindicator value updated on the basis of the time difference of saidreceiving moments exceeds a predetermined threshold value.

In a method according to an embodiment of the invention, the qualityclassification associated with the second ingress port and used by aquality classification aware routing protocol is downgraded if saidfirst protocol data unit, received at an earlier point of time, is laterin said sequential order than said second protocol data unit, receivedat a later point of time, and an indicator value updated on the basis ofthe time difference of said receiving moments exceeds a predeterminedthreshold value.

The procedure applied in the update of said indicator value can bechosen in several different ways. In a procedure according to a firstexample, said time difference between the receiving moments is as suchused as said indicator value. In a procedure according to a secondexample, said time difference between the receiving moments is comparedto said indicator value and if said time difference between thereceiving moments and a predetermined number of time differencescalculated earlier are greater than said indicator value, said timedifference is set as a new indicator value. In a procedure according toa third example, said time difference between the receiving moments isused as an input quantity for low-pass filtering and an output quantityof said low-pass filtering is the indicator value.

In a method according to an embodiment of the invention, said firstprotocol data unit and said second protocol data unit are one of thefollowing: IP (Internet Protocol) packets, ATM (Asynchronous TransferMode) cells, Ethernet units, or Frame Relay units.

In a method according to an embodiment of the invention, the orderindicator associated with each protocol data unit is one of thefollowing: transmission time stamp indicating the transmitting moment ofthe protocol data unit in question, and an ordinal number of theprotocol data unit in question.

A computer program according to an embodiment of the invention comprisessoftware means for controlling a programmable processor to determine themutual differences of the transmission delays experienced by protocoldata units received, wherein each protocol data unit is associated withan order indicator arranged to indicate the position of the protocoldata unit in the mutual sequential order of said protocol data units,and each protocol data unit is sent earlier than or simultaneously withthe protocol data unit next in said sequential order. Said softwaremeans comprises:

-   -   software means for controlling said programmable processor to        determine, based on a first order indicator associated with a        first protocol data unit received earlier and a second order        indicator associated with a second protocol data unit received        later, whether the first protocol data unit comes later in said        sequential order than said second protocol data unit, and    -   software means for controlling said programmable processor to        calculate, in response to a situation in which said first        protocol data unit comes later in said sequential order than        said second protocol data unit, the time difference of the        receiving moments of said second protocol data unit and said        first protocol data unit, said time difference representing the        smallest possible difference between the transmission delays        experienced by said second protocol data unit and said first        protocol data unit.

Said software means may be e.g. subroutines or functions. Saidprogrammable processor may be the processor unit 308 shown in FIG. 3,for example.

A computer program according to an embodiment of the invention is storedon a storage medium, such as an optical compact disk (CD), readable bythe programmable processor.

A computer program according to an embodiment of the invention is codedinto a signal which can be received via a communications network such asthe Internet, for example.

As is obvious to a person skilled in the art, the invention and itsembodiments are not limited to the exemplary embodiments depicted above,but the invention and its embodiments can be modified within the scopeof the independent claim. Expressions used in the claims describing theexistence of characteristic features, such as “the arrangement has aprocessor unit” are non-exclusive such that a mention of acharacteristic feature shall not exclude the existence of othercharacteristic features not mentioned in the independent or dependentclaims.

What is claimed is:
 1. An arrangement for determining mutual differencesof transmission delays experienced by received protocol data units andfor performing control actions related to ingress ports of a networkelement, each protocol data unit being associated with an orderindicator arranged to indicate the position of that protocol data unitin a mutual sequential order of said protocol data units, and eachprotocol data unit being sent earlier than or simultaneously with aprotocol data unit next in said sequential order, the arrangementcomprising a processor unit arranged to: determine, based on a firstorder indicator associated with a first protocol data unit receivedearlier and a second order indicator associated with a second protocoldata unit received later, whether the first protocol data unit is laterin said sequential order than said second protocol data unit, said firstprotocol data unit being a protocol data unit received at a firstingress port of the network element, and said second protocol data unitbeing a protocol data unit received at a second ingress port of saidnetwork element, and in response to a situation in which said firstprotocol data unit is later in said sequential order than said secondprotocol data unit, calculate a time difference of receiving moments ofsaid second protocol data unit and said first protocol data unit, saidtime difference representing a lower limit for a difference betweentransmission delays experienced by said second protocol data unit andsaid first protocol data unit, wherein said processor unit is furtherarranged to downgrade a quality classification associated with saidsecond ingress port and used by a quality classification aware routingprotocol in response to a situation where said first protocol data unitis later in said sequential order than said second protocol data unitand an indicator value updated on the basis of said time differenceexceeds a predetermined threshold value.
 2. An arrangement according toclaim 1, wherein said first ingress port is a physical ingress port or alogical ingress port and said second ingress port is a physical ingressport or a logical ingress port.
 3. An arrangement according to claim 1,wherein said processor unit is arranged to compare said time differencewith said indicator value and to set said time difference as saidindicator value in response to a situation where said time differenceand a predetermined number of corresponding time differences calculatedearlier are greater than said indicator value.
 4. An arrangementaccording to claim 1, wherein said processor unit is arranged to usesaid time difference as an input quantity for low-pass filtering, anoutput quantity of said low-pass filtering being said indicator value.5. An arrangement according to claim 1, wherein said first protocol dataunit and said second protocol data unit are one of the following: IP(Internet Protocol) packets, ATM (Asynchronous Transfer Mode) cells,Ethernet units, or Frame Relay units.
 6. An arrangement according toclaim 1, wherein said order indicator associated with each protocol dataunit is one of the following: transmission time stamp indicating thetransmitting moment of the protocol data unit in question, and anordinal number of the protocol data unit in question.
 7. A networkelement comprising: a first ingress port and a second ingress port forreceiving protocol data units each of which is associated with an orderindicator arranged to indicate the position of that protocol data unitin a mutual sequential order of said protocol data units, and each ofwhich is sent earlier than or simultaneously with the protocol data unitnext in said sequential order, a processor unit arranged to: determine,based on a first order indicator associated with a first protocol dataunit received earlier and a second order indicator associated with asecond protocol data unit received later, whether the first protocoldata unit is later in said sequential order than said second protocoldata unit, said first protocol data unit being a protocol data unitreceived at the first ingress port of the network element, and saidsecond protocol data unit being a protocol data unit received at thesecond ingress port of the network element, in response to a situationin which said first protocol data unit is later in said sequential orderthan said second protocol data unit, calculate a time difference ofreceiving moments of said second protocol data unit and said firstprotocol data unit, said time difference representing a lower limit fora difference between transmission delays experienced by said secondprotocol data unit and said first protocol data unit, and downgrade aquality classification associated with said second ingress port and usedby a quality classification aware routing protocol in response to asituation where said first protocol data unit is later in saidsequential order than said second protocol data unit and an indicatorvalue updated on the basis of said time difference exceeds apredetermined threshold value.
 8. A network element according to claim7, wherein the network element is one of the following: an IP (InternetProtocol) router, Ethernet switch, ATM (Asynchronous Transfer Mode)switch, base station of a mobile communications network, or an MPLS(Multi Protocol Label Switching) switch.
 9. A method for determiningmutual differences of transmission delays experienced by receivedprotocol data units and for performing control actions related toingress ports of a network element, each protocol data unit beingassociated with an order indicator arranged to indicate the position ofthat protocol data unit in a mutual sequential order of said protocoldata units, and each protocol data unit being sent earlier than orsimultaneously with the protocol data unit next in said sequentialorder, the method comprising: determining, based on a first orderindicator associated with a first protocol data unit received earlierand a second order indicator associated with a second protocol data unitreceiver later, whether the first protocol data unit is later in saidsequential order than said second protocol data unit, said firstprotocol data unit being a protocol data unit received at a firstingress port of the network element and said second protocol data unitis a protocol data unit received at a second ingress port of the networkelement, in response to a situation in which said first protocol dataunit is later in said sequential order than said second protocol dataunit, calculating a time difference of receiving moments of said secondprotocol data unit and said first protocol data unit, said timedifference representing a lower limit for a difference betweentransmission delays experienced by said second protocol data unit andsaid first protocol data unit, and downgrading a quality classificationassociated with said second ingress port and used by a qualityclassification aware routing protocol in response to a situation wheresaid first protocol data unit is later in said sequential order thansaid second protocol data unit and an indicator value updated on thebasis of said time difference exceeds a predetermined threshold value.10. A method according to claim 9, wherein said first ingress port is aphysical ingress port or a logical ingress port and said second ingressport is a physical ingress port or a logical ingress port.
 11. A methodaccording to claim 9, wherein said time difference is compared to saidindicator value and if said time difference and a predetermined numberof corresponding time differences calculated earlier are greater thansaid indicator value, said time difference is set as a new indicatorvalue.
 12. A method according to claim 9, wherein said time differenceis used as an input quantity for low-pass filtering, an output quantityof said low-pass filtering being said indicator value.
 13. A methodaccording to claim 9, wherein said first protocol data unit and saidsecond protocol data unit are one of the following: IP (InternetProtocol) packets, ATM (Asynchronous Transfer Mode) cells, Ethernetunits, or Frame Relay units.
 14. A method according to claim 9, whereinsaid order indicator associated with each protocol data unit is one ofthe following: transmission time stamp indicating the transmittingmoment of the protocol data unit in question, and an ordinal number ofthe protocol data unit in question.
 15. A non-transitory computerreadable medium encoded with a computer program for controlling aprogrammable processor to determine mutual differences of transmissiondelays experienced by protocol data units received and to performcontrol actions related to ingress ports of a network element, eachprotocol data unit being associated with an order indicator arranged toindicate the position of that protocol data unit in a mutual sequentialorder of said protocol data units, and each protocol data unit beingsent earlier than or simultaneously with the protocol data unit next insaid sequential order, the computer program comprising: software meansfor controlling said programmable processor to determine, based on afirst order indicator associated with a first protocol data unitreceived earlier and a second order indicator associated with a secondprotocol data unit received later, whether the first protocol data unitis later in said sequential order than said second protocol data unit,said first protocol data unit being a protocol data unit received at afirst ingress port of the network element to be controlled, and saidsecond protocol data unit being a protocol data unit received at asecond ingress port of the network element, software means forcontrolling said programmable processor to calculate, in response to asituation in which said first protocol data unit is later in saidsequential order than said second protocol data unit, a time differenceof receiving moments of said second protocol data unit and said firstprotocol data unit, said time difference representing a lower limit fora difference between the transmission delays experienced by said secondprotocol data unit and said first protocol data unit, and software meansfor controlling said programmable processor to downgrade a qualityclassification associated with said second ingress port and used by aquality classification aware routing protocol in response to a situationwhere said first protocol data unit is later in said sequential orderthan said second protocol data unit and an indicator value updated onthe basis of said time difference exceeds a predetermined thresholdvalue.